It is very reliable. It is 12 years old and over 100k miles and still drives smoothly.
I just purchased my 2006 Sienna this past January, as we were expecting our 3rd child. I love the amount of space in my van. I especially like the split bench as the 3rd row seat. This still allows us to have our oldest child's car seat in the back row, but also be able to fold down the other part of the seat to fit the stroller or other items. Even though the van is 12 years old, it runs great. Also, I LOVE all of the extra compartments! I do wish that both of my sliding doors and the back door were push button, but I know the newer models have that option.